This invention relates to an ultrasound system and method for synthetic aperture processing. In particular, the system adjusts a beam width.
Ultrasound systems generate two-dimensional images representing a region of the subject under examination. Many ultrasound systems are capable of generating images representing three dimensions of a volume region of the subject under examination. The three-dimensional representations are generated from a plurality of frames of data associated with a respective plurality of two-dimensional regions.
Any of various transducers are used for transmitting and receiving acoustic energy for scanning a two-dimensional region. For example a linear transducer is used. A linear transducer includes a plurality of transducer elements spaced along an azimuth or lateral dimension. Acoustic energy is fired along a series of ultrasound lines that are electronically steered along the azimuth dimension. The ultrasound system samples data along each ultrasound line, defining an axial or range dimension. To obtain additional two-dimensional (i.e., azimuth and axial dimensions) images, the transducer is repositioned along the elevation dimension.
In the range-azimuth plane, resolution is a function of the temporal width of the two-way acoustic pulse (i.e., the axial resolution) and the lateral beam width at the point of interest within the two dimensions. Generally, the axial resolution is constant throughout the image. The lateral beam width or lateral resolution may be kept constant throughout the image by focusing and dynamically controlling the receive aperture, compensating for the fixed focus of the transmit beam.
For many transducers, the resolution associated with the elevation dimension is a function of the acoustic lens design or the surface shape of the PZT (i.e., mechanically focused wavefront). For example, the acoustic lens provides a fixed focal depth and elevation beam width as a function of the wavelength of the acoustic pulse. Due to the fixed focus, the resolution is better at the point of focus then at other axial positions, such as the near-field or far-field. For imaging, the elevational resolution undesirably varies as a function of the axial position within an image.
Using a 1.5 or a two-dimensional transducer, the elevation aperture and resulting elevation resolution may be electronically controlled. For example, the elevation aperture is controlled in a similar methodology as for the azimuthal aperture with a linear transducer. However, 1.5 and two-dimensional transducers are more costly and complicated.
In radar imaging, satellites or other radio frequency transmitters transmit beams to different locations within a grid to generate an image, such as an image of terrain. The transmitters act as a single or other limited element array. Multiple beams are transmitted for imaging a respective multiple points along the grid. To account for the small aperture size, synthetic aperture radar (SAR) processes were developed. The data received from the multiple transmissions is processed to account for the single element transmission. For example, the phase associated with multiple transmissions is adjusted.